A large variety of articles are made in which precious metals are used as a protective coating. Particularly well known are jewelry articles where precious metal films are used to improve appearance and protect the surface from corrosion and discoloration. In many other applications, precious metal coatings are used for surface protection to prevent corrosion and at times to serve as a diffusion barrier as for example in the fabrication of various semiconductor devices. For various electrical and electronic devices, precious metal films are used for electrical conduction paths. In other electrical and electronic devices precious metal films are used as electrical contact surface. Gold is used in these applications with great success. However, it is highly desirable to obtain a material, equally effective as gold, which is less expensive and which can be electroplated faster and with greater ease.
Palladium and palladium alloys are used in a number of applications where chemical inertness, bright finish and high electrical conductivity are required. Palladium is used as a diffusion barrier in various applications, often as part of an electrode structure or electrical contact structure. Palladium metal and alloys are used as a protective coating on jewelry and various other articles. Palladium metal and alloys are also used in the electrical arts on contact surfaces, as electrical conduction paths and in optical devices.
Particularly attractive is the use of palladium and palladium alloys as electrical contact surfaces in the electrical arts. Palladium and palladium alloys are chemically inert, are hard and wear well and have good electrical conductivity. In addition, palladium and palladium alloys do not form oxide surface coatings that might increase surface contact resistance. Typical applications for electrical contact material are in electrical connectors, relay contacts, switches, etc. Various palladium alloys such as palladium-silver, palladium-nickel and palladium-copper are also useful in these applications. Indeed, where low cost is highly important, various palladium alloys such as palladium-nickel and other palladium alloys are often preferred. Particularly desirable is a process for electroplating palladium and palladium alloys from aqueous solutions which is rapid, inexpensive, easy to operate under manufacturing conditions and yields palladium and palladium alloy films that are ductile, adherent and free from hydrogen. In addition, in many applications, it is desirable that the bath not attack the metal being plated so that the bath remains uncontaminated over long periods of time. Also highly desirable is an alloy electroplating process in which the metal composition of the bath is close to the composition of the alloy being electroplated so that bath metal composition can be controlled during the electroplating process.
Palladium electroplating processes have been described in a number of references including U.S. Pat. No. 4,486,274 issued to J. A. Abys et al on Dec. 4, 1984. Also, references cited in this case such as U.S. Pat. No. 4,066,517 issued to Stevens et al in January 1978; U.S. Pat. No. 4,278,514 issued to Morrissey in July 1981 and U.S. Pat. No. 4,339,311 issued in July 1982 describe palladium electroplating processes but do not disclose the bath composition disclosed and claimed in the instant application.